1. Field of the Invention
The present invention relates to a flat fiber bundle and to a method and an apparatus for manufacturing the same.
2. Description of the Related Art
In the case where non-twisted multifilament (long staple fiber) yarns (fiber bundle) are used as reinforcement fibers for producing a fiber reinforced composite structure, there is a method such as a filament winding method wherein a fiber bundle is impregnated with a solution of resin and wound on a mandrel, and the resin is then cured. There is also a method wherein a three-dimensional woven fabric (three-dimensional fibrous structure) is formed of fiber bundles, impregnated with a solution of resin, and the resin is then cured.
When the non-twisted fiber bundle is wound, for example, on the mandrel, the fiber bundle is wound in a flat condition due to a winding force. Similarly, when the three-dimensional fibrous structure is manufactured, a fibrous layer constituting the three-dimensional fibrous structure is compressed for the purpose of increasing the content of reinforcement fibers per unit volume, whereby the fiber bundle becomes flat in shape.
In the case where the fiber reinforced composite structure is manufactured by the filament winding method, or when the three-dimensional fibrous structure is used as a reinforcement material of the fiber reinforced composite structure, it is preferable to arrange the fiber bundles in an opened state from the beginning to ensure physical properties of the resultant composite structure. In this regard, the opened state refers to a state wherein filaments constituting the fiber bundle are spread in the widthwise direction to flatten the fiber-bundle.
In the filament winding method or the method for the production of three-dimensional fibrous structure, since the fiber bundle is unwound from the bobbin, it is necessary to join the fiber bundle on the bobbin to a fiber bundle on the next bobbin before the former has been completely exhausted. If the fiber bundles are joined by forming a knot as in the piecing of ordinary yarns, knots remain in the resultant product in a non-opened state and the physical property of the product is deteriorated. Therefore, a method has been proposed wherein ends of fiber bundles are joined together, by the entanglement of filaments, without using knotting.
For example, Japanese Unexamined Patent Publication (Kokai) No. 51-147569 discloses a method for joining strands of a plurality of continuous fibers by overlapping ends of the strands with each other and applying an air stream to the overlapped portion to cause the filaments therein to be entangled with each other. The joining apparatus used for this purpose is shown in FIG. 16A in the attached drawings, and comprises a tubular casing 81 having a substantially vertical air inlet port 82 positioned in the casing at the center thereof, a pair or more of air exit ports 83 on the opposite ends of the casing, and a pair of gripper sections 85 for gripping strands 94 so that the center of the overlapped portion of the strands is at the center of the casing.
Also, Japanese Unexamined Patent Publication (Kokai) No. 6-100246 discloses an apparatus for joining fiber bundles wherein ends of two fiber bundles are overlapped with each other and air is injected to the overlapped portion to cause filaments forming the fiber bundles to be entangled, as shown in FIG. 17 of the attached drawings. This apparatus comprises an apparatus body 86 having a supporting section 89, and a cover plate 88 coupled to the apparatus body 86 by a hinge 87. A plurality of elongated flow control plates 90 are arranged on the supporting section 89 in parallel to each other at a predetermined interval so that the short sides thereof extend vertically. The outermost flow control plate 90 is slightly higher than the others.
The cover plate 88 is provided with a rectangularly annular fiber holding member 92 having an air blowing window 91. The fiber holding member 92 is provided with a plurality of pressing thin rods 94 fixed at opposite ends thereof to a pair of support rods 93 arranged parallel to the flow control plates 90, and an air injection nozzle 95. The air injection nozzle 95 is movable in the direction perpendicular to the flow control plates 90. Two fiber bundles (not shown) are placed on the support section 89 with the ends thereof in an overlapped state and after the cover plate 88 is placed on the apparatus body 86, the fiber bundles are joined together by injecting air from the air ejection nozzle 95 which is moved in the direction perpendicular to the flow control plates 90.
In the joining method disclosed in Japanese Unexamined Patent Publication No. 51-147569, portions of the joined strands in the vicinity of the gripped portions are narrowed, as shown in FIG. 16B, since the joining operation is carried out by rotating the portion of the strands in the tubular casing 81 as a whole by the turbulent air stream impinging on the central region of the strands. Filaments in the narrowed portions are difficult to open, and if such a joined region is inserted and mixed in the resultant composite structure, a matrix-rich portion is generated to deteriorate the physical property of the manufactured product. If the narrowed portions are in a state to be readily opened, the connecting strength is lowered.
On the contrary, in the method disclosed in Japanese Unexamined Patent Publication No. 6-100246, the fiber bundles to be joined are acted on by air while the ends of fiber bundles are in a free condition and portions of the fiber bundles adjacent to the overlapped portion are held. The fibers are prevented from moving in the lateral direction (perpendicular to the lengthwise direction of the filaments), by the action of the flow control plates 90, and the filaments are entangled with each other without dispersing in the lateral direction, resulting in the improvement of the withdrawing strength. However, since the fiber bundles are subjected to the air action while the ends of the fiber bundles are in a free state, the orientation of the filaments in the joined region is largely disturbed, and the physical property of the resultant composite, structure is deteriorated.
Also, in the prior art, there is a three-dimensional fibrous structure for reinforcing a composite structure formed by a plurality of cloth sheets superposed on each other with a fastening thread. The cloth sheet is convenient for handling and is easily laid on a curved surface. However, since at least one of warp yarns and weft yarns forming the cloth sheet are arranged in a meandering manner, the physical property of the resultant composite structure is deteriorated in comparison with that using a reinforcement material in which filaments forming each of layers are linearly arranged. Accordingly, if there was a one-directional material convenient in handling such as the cloth sheet and having filaments linearly arranged in one plane, a three-dimensional structure excellent in physical property would be easily obtainable.
The present invention has been made in view of the above-mentioned problems in the prior art, and the first object of the present invention is to provide a fiber bundle which can be easily handled and which is formed by joining a plurality of flat fiber bundles of non-twisted filaments, wherein filaments in the joined region of the fiber bundles are movable in the direction perpendicular to the filament-extending direction to have a large degree of freedom in shape but not too loose.
The second object of the present invention is to provide a method for joining fiber bundles.
The third object of the present invention is to provide a method for joining two flat fiber bundles of non-twisted filaments so that a degree of freedom in the shape is large even in the joined region and the ease of handling is not lowered.
The fourth object of the present invention is to provide an apparatus for joining fiber bundles in accordance with the above-mentioned method.
In addition, the fifth object of the present invention is to provide a flat fiber bundle of non-twisted filaments capable of expanding and contracting in the direction perpendicular to the filament-extending direction but not randomly separate from each other.
The sixth object is to provide a method for manufacturing such a fiber bundle.
To achieve the first object, a fiber bundle according to the present invention is manufactured by holding a plurality of flat fiber bundles of non-twisted filaments (long staple fibers) arranged in a first direction in an at least partly overlapped relationship or in a parallel and adjoining relationship at two points spaced apart from each other in the first direction, and injecting gas to the fiber bundles between the two points at a plurality of positions viewed in a second direction transverse to the first direction to cause the adjacent filaments to be entangled with each other.
Thus, the obtained fiber bundle is expandable and contractible in the direction perpendicular to the first, filament-extending direction even in the joined region, and is not too loose, i.e., it is difficult to separate the individual filaments from each other. As a result, the ease of handling is improved.
Preferably, the plurality of flat fiber bundles are arranged in parallel to each other so that a sheet is formed by the entanglement of adjacent filaments. Thus, the inventive fiber bundle is suitable for forming a one directional material by being impregnated with resin therein or producing a three-dimensional fibrous structure by superposing the sheets instead of cloth sheets.
To achieve the second object, a method for joining fiber bundles according to the present invention comprises the steps of holding a plurality of flat fiber bundles of non-twisted filaments arranged in a first direction in an at least partly overlapped relationship or in a parallel and adjoining relationship, at two points spaced apart from each other in the first direction, and injecting gas to the fiber bundles between the two points at a plurality of positions, viewed in a second direction transverse to the first direction, to cause the adjacent filaments to be entangled with each other.
In this arrangement, since the fiber bundles are subjected to the gas injection while being held at two points spaced apart from each other in the filament-extending direction, the filaments are rotated with the gripped portions functioning as fulcrums and entangled with each other. Accordingly, the filaments are arranged basically in the lengthwise direction of the fiber bundle even in the joined region.
To achieve the third object, the plurality of fiber bundles are preferably two flat fiber bundles, and ends of the fiber bundles are joined together under the condition wherein the ends are overlapped with each other. Thus, the two flat fiber bundles are maintained in a flat state even in the joined region so that it is expandable and contractible in the widthwise direction and has a large degree of freedom in shape even in the joined region, whereby the ease of handling becomes equal to that of a single fiber bundle.
Preferably, the ends of the fiber bundles are overlapped with each other so that the fiber bundle located closer to the gas-injection side is slack. Thus, since the filaments located closer to the gas-injection side are subjected to the gas-injection, a moving range of the filaments becomes larger when they are rotated about the gripped portions defining the fulcrums to enhance the entanglement thereof with those farther from the gas-injection side and the tensile strength is enhanced.
Preferably, when the ends of both the fiber bundles are overlapped, the end portions of the fiber bundles to be overlapped with each other are wider in comparison with the remaining portions of the fiber bundles and gas is injected to the overlapped portion to join the fiber bundles together, and thereafter the overlapped portion is folded so that the width of the folded portion becomes half of the width of the fiber bundle before folding, the gas is injected in the same manner as described above under the condition wherein the overlapped portion is held at two points spaced apart from each other in the filament-extending direction to cause the filaments to be entangled in the overlapped portion.
In this arrangement, when the two fiber bundles are joined together, portions to be overlapped are first widened, for example, the width is spread to about 1.5 to 2 times of the width of the other portions, and then gas is injected to join the fiber bundles together. Next, the overlapped portion is folded so that the width of the folded fiber bundle becomes half of the width of the fiber bundle before folding, and gas is injected to the overlapped portion while holding two points spaced apart from each other in the filament-extending direction to join the fiber bundles together. Thus, one of the free ends of the fiber bundles appears on the outer surface of the joined region when the gas is injected with two fiber bundles are simply overlapped with each other, and that one end is positioned in the joined region when the second joining operation is carried out. Therefore, it is possible to assuredly prevent the filament end from turning up when the joined portion of the fiber bundles passes through a guide bar or a supply head.
Preferably, the plurality of fiber bundles are arranged in parallel to each other and suitably subjected to the above-described entanglement treatment by the gas injection so that the adjacent filaments are entangled to each other to form a sheet. Thus, the fiber bundle can be easily produced.
To achieve the fourth object, a fiber bundle joining apparatus according to the present invention comprises a base having a pair of support sections spaced apart from each other in a first direction for supporting ends of flat fiber bundles, a gripper having gripping sections for cooperation with the support sections and moved by an actuator between a gripping position where the fiber bundles are gripped by the gripper and the support sections and a retreating position where the fiber bundles are released, a movable member disposed in the base and movable relative to the base in a second direction transverse to the first direction, a presser provided in the movable member and movable between an operating position where it is capable of pressing the fiber bundles supported by the support sections and a retreated position where it allows the fiber bundles to be rested on the support sections, a nozzle provided in the movable member so that a position thereof opposed to the fiber bundles gripped by the support sections and the gripper is variable as the movable member moves relative to the base, and a returning member for returning the movable member to a reference position.
In this arrangement, when two fiber bundles are joined together, the ends of two fiber bundles extending over the support sections of the base with the presser inserted between them, and are held by the gripper located at the gripping position and the support sections. In this state, gas is injected from the orifice of the nozzle and the movable member moves from the reference position relative to the base in the direction transverse to the fiber bundles. The presser moves together with the movable member, and gas is injected from the nozzle to the fiber bundles at a position from which the presser is retreated from the fiber bundles. The overlapped portion of fiber bundles, the ends of which are nipped between the support sections and the gripper, are made to rotate about the gripped portions defining fulcrums, and are entangled with each other.
Preferably, the gripper is provided with a regulating member located in the vicinity of the gripped fiber bundles for covering the entire portion of the fiber bundles between the support sections when the gripper is located at the gripping position. Thus, according to this embodiment, the gas flow injected from the nozzle changes its direction by the regulating member into the widthwise direction of the fiber bundles, whereby the rotation of filaments about the gripped portions defining fulcrums is facilitated, whereby the strength of the joined portion increases.
To achieve the fifth object, the flat fiber bundles of non-twisted filaments are provided, wherein the adjacent filaments are entangled with each other at a predetermined interval in the filament-extending direction. Thus, the fiber bundle is expandable and contractible in the direction perpendicular to the filament-extending direction, but the filaments thereof are not too loose, whereby the fiber bundle can easily conform to a complicated profile such as a curved surface.
To achieve the sixth object, a method of manufacturing a fiber bundle is provided wherein a single flat fiber bundle of non-twisted filaments is held at two points spaced apart from each other in a filament-extending direction, gas is injected to the fiber bundle between the two points at a plurality of positions viewed in a direction transverse to the filament-extending direction to cause the adjacent filaments to be entangled, and the holding step and the injecting step are performed while displacing the injecting positions in the filament-extending direction.